A gear shaving machine equipped with a shaving cutter is used to finish the tooth flanks of a gear to be processed (hereinafter referred to as a workpiece gear), which has been gear-cut by a gear cutting machine (hobbing machine, gear shaping machine), to even more accurate ones.
The shaving cutter is a gear-shaped tool, which is meshed with a workpiece gear to finely cut the tooth flanks of the workpiece gear, thereby finishing (shaving) the tooth flanks. For this purpose, the tooth profile of the shaving cutter is formed in a shape corresponding to the aimed shape of the workpiece gear to be shaved.
After such a shaving cutter has shaved a plurality of workpiece gears, the tooth flanks of the shaving cutter wear out. Thus, the tooth profile of the shaving cutter needs to be regenerated so as to assume a shape corresponding to the aimed shape of the workpiece gear. That is, the worn-out shaving cutter needs to be sharpened.
If the shaving cutter wears out, this shaving cutter is detached from the gear shaving machine.
To regenerate the tooth profile of the shaving cutter so as to become a shape corresponding to the aimed shape of the workpiece gear, it is common practice to mount the shaving cutter on a shaving-cutter grinding machine and grind the shaving cutter for regeneration.
The shaving-cutter grinding machine has a rotating disk-shaped grindstone as a tool for grinding the shaving cutter. This shaving-cutter grinding machine imparts a gear-generating movement to the shaving cutter meshing with the disk-shaped grindstone to grind the tooth flanks of the shaving cutter, thereby sharpening the shaving cutter.
With the shaving-cutter grinding machine, as the grinding of the shaving cutter proceeds, the grindstone wears and its sharpness decreases. Thus, after grinding a plurality of shaving cutters successively, the worn-out grindstone is dressed to regenerate or newly create sharp tooth flanks. For dressing, a dresser device is used, and shaving-cutter grinding machines equipped with dresser devices are provided in large numbers.
The shaving-cutter grinding machine equipped with the dresser device has
(1) a phase in which the grindstone grinds the shaving cutter, and
(2) a phase in which the dresser device dresses the grindstone.
The status of the transfer of the tooth profile is summarized as follows:
In the shaving-cutter grinding machine, the shape of the grindstone having tooth flanks of a predetermined shape formed therein as a result of dressing by means of the dresser device is transferred to the shaving cutter. That is, the shaving cutter is ground by the grindstone, whereby sharpening of the shaving cutter takes place.
This shaving cutter is installed in a gear shaving machine to shave a workpiece gear, thereby transferring the shape of the shaving cutter to the workpiece gear.
That is, the tooth profile is transferred in the following sequence: grindstone of shaving-cutter grinding machine→shaving cutter→workpiece gear.
As described above, the tooth profile is transferred in the following sequence: grindstone of shaving-cutter grinding machine→shaving cutter→workpiece gear. Thus, in order that the tooth profile of the gear after shaving will become the targeted tooth profile, the grindstone is dressed to set the shape of the grindstone.
If the tooth profile of the gear after shaving deviates from the targeted tooth profile, dressing is carried out to eliminate this deviation, whereby the shape of the grindstone must be modified.
Thus, a method has been developed which, if the tooth profile of the gear after shaving deviates from the targeted tooth profile, performs dressing so as to eliminate this deviation, thereby modifying the shape of the grindstone (see, for example, Patent Document 1).
With the technology shown in Patent Document 1, the modification of the grindstone shape has been made in the following manner:
(1) Measure the shaved gear to obtain measured tooth-profile data (Dm).
(2) Find tooth-profile error data (ΔD) which is the difference (Do−Dm) between target tooth-profile data (Do) showing the targeted tooth profile and the measured tooth-profile data (Dm) after shaving.
(3) Based on the tooth-profile error data (ΔD) and the target tooth-profile data (Do), obtain aimed tooth-profile data (Dc).
If the correction coefficient is set at α, for example, a computation Dc=Do+α·ΔD is performed to obtain the aimed tooth-profile data (Dc).
(4) Carryout an operation for data conversion of the aimed tooth-profile data (Dc) to obtain shaving-cutter tooth-profile data (ds).
(5) Control the dressing device to dress the grindstone so that the grindstone will have a grindstone surface shape to which the tooth profile of the shaving cutter specified by the shaving-cutter tooth-profile data (ds) has been transferred.
Upon modification of the grindstone surface shape of the grindstone in the above-described manner, the shaving cutter is ground with the so modified grindstone to sharpen the shaving cutter, whereby the tooth profile of the shaving cutter becomes an appropriate shape. Thus, the shaving cutter whose tooth profile has been modified to achieve the appropriate shape is mounted on the gear shaving machine, and the workpiece gear is shaved thereby. As a result, the tooth profile of the workpiece gear after shaving becomes the targeted tooth profile.
Each time the sharpening work of grinding the shaving cutter with the grindstone to sharpen the shaving cutter is done, the outer diameter and the tooth thickness of the shaving cutter decrease by amounts corresponding to the grinding. Furthermore, as the number of times the sharpening is performed increases, the amounts of the decreases in the outer diameter and the tooth thickness of the shaving cutter increase.
Thus, the technique of modifying the grindstone shape shown in Patent Document, if used alone, has caused the tooth profile of the gear after shaving to deviate from the targeted tooth profile. The larger the number of times the sharpening takes place, in particular, the greater such a problem becomes.
To obtain a more accurate tooth profile, therefore, it is necessary to further modify the aimed tooth-profile data (Dc) in accordance with the number of times the sharpening is carried out, thereby finding the modified aimed tooth-profile data (Dc′), in consideration of the fact that the outer diameter and tooth thickness of the shaving cutter decrease as a result of sharpening.
The modified aimed tooth-profile data (Dc′) is subjected to an operation for data conversion to find shaving-cutter tooth-profile data (ds). In order that the grindstone will have a grindstone surface shape to which the tooth profile of the shaving cutter specified by the shaving-cutter tooth-profile data (ds) has been transferred, the dressing device is controlled to dress the grindstone.